Electric rheostat or heater.



No. 707,|94. Patented Aug. l9, I902.

H. P. BALL.-

ELECTRIC BHEOSTAT 0R HEATER.

(Application filed Nov. 2, 1896.)

(No Model.)

M/ VE/VTOI? A ITO/MUS- UNITED STATES PATENT OFFICE.

HENRY PRICE BALL, OF BROOKLYN, NEIV YORK, ASSIGNOR, BY MESNEASSIGNMENTS, TO II. IVARD LEONARD, OF BRONXVILLE, NEl/V YORK.

ELECTRIC RHEOSTAT OR HEATER.

SPECIFICATION forming part of Letters Patent No. 707,194, dated August19, 1902.

Application filed November 2, 1896. Serial No. 610,795. (No model.)

To all whom it may 0012007 12,;

Be it known that I, HENRY PRICE BALL, a citizen of the United States,residing inthe city of Brooklyn, in the county of Kings and State of NewYork, have invented certain new and useful Improvements in ElectricRheostats or Heaters, of which the following is a specification,reference being had to the accompanying drawings, forming a part hereof.My invention relates to devices in which electric energy is convertedinto heat. Such a device, whether a rheostat or an electric heater,should be so constructed that there shall be a maximum conductor-surfacein order that it may have the greatest amount of surface for radiatingheat or imparting heat to the radiating part of the device. Theconductor should also be of as high specific resistance as obtainable,the other properties of the conductor being equally good, such as itsnon-oxidation at any but a high temperature, if at all. Furthermore, theconductor, particularly if small and of little mechanical strength,should be supported or held so that it cannot shake or vibrate or sagout of position. The supporting-body for the conductor acts as theradiating part of the device, and it will be seen then that the heatgenerated in the conductor must pass first from the conductor to theinsulation between the conductor and the support and then through thesupport to the radiating-surface, so that it is very necessary to havethe thickness of insulation between the conductor and the support aminimum and the thickness of the support also a minimum, while theradiating surface is a maximum, and the extent of contact between theconductor and the insulation and between the insulation and the supportis a maximum. The entire device, outside of the conductor, should be asgood a conductor of heat as practicable in order that the heat may bequickly conducted from the conductor or heat-generator to thedissipating or radiating surface, and it is desirable to so constructthe device that when it is unequally loadedthat is to say, when one partof the device is generating more heat than anotherthe supporting partshall equalize or distribute the heat over the entire or greater part ofthe radiating-surface, thereby reducing the temperature of the deviceand permitting the device to be made smaller than otherwise would bepossible. I attain all of these advantages by my invention, which isfully described hereinafter and is illustrated in the accompanyingdrawings, in which-'- Figure 1 is a side view of a rheostat or heaterconstructed in accordance with my invention. Fig. 2 is an edgewise viewof the same looking at Fig. 1 from the right, partly in verticalsection. Fig. 3 is a horizontal section of the same. Fig. 4 is a viewsimilar to Fig. 3, but showing a slightly-different form of the support.Fig. 5 is a partial View, in vertical section, showing another form ofthe support, which may be employed where radiation from one side only isdesired. Fig. 6 is a partial horizontal section similar to Figs. 3 andat, showing still another form of the support.- Fig. 7 is a transversesectional view illustrating a different embodiment of a feature of theinvention.

In the constructions shown in Figs. 1, 2, 3, and i the support for theconductor or resistance 3 is represented as composed of two parts 1 and2, which are formed of reflexed or corrugated sheet-iron or copper orother suitable material, the corrugations being such that when the partsare laid together and secured face to face by rivets 4 or otherwise theoppositely-concave portions of the sheet or support form a number ofparallel receptacles .or spaces, substantially tubular, into which theparallel conductors or resistances 3 can be placed and by, which theyare supported. As an insulating material between the conductor 3 and thesupporting shells or plates 1 and 2 I use enamel or mica or any materialthat can be used in a thin layer, enamel having the advantage that itcan be placed all over the supporting shells or plates, both inside andout, as indicated at 5 and 6, thereby reducing the liability of a groundfrom any connecting-wire accidentally touching the outside of thesupporting-plates.

It will be seen that by the use of corrugated sheet metal, whichconforms substantially to the general shape of the resistances, I havethe same distance at all places for the heat to travel from theconductor to the radiating surface, while at the same time theradiatingsurface is greatly increased by the use of the corrugatedsurface. The corrugations therefore serve a double purpose, that ofholding.

the resistance on one side of the sheet and that of radiating ordissipating the heat on the other, while at the same time there is aminimum of material, and therefore the least possible difference oftemperature between the conductor and the radiating surface. Theconductor 3 may be inserted into the holder or receptacle in acontracted state and then allowed to revolve and expand into the spacesprovided. This brings the conductor into touch with the insulationbetween it and the support, and the heat is rapidly drawn off. As shownin Fig. 4, the radiatingsurface may be further increased by crimping thematerial of the support, as represented at 7.

In some instances it might be advisable to cause the wire to adhere atall points along its length to the support. In such cases I cover theconductor with a layer of enamel, which being fused to the enamel thatis under the conductor envelops or embeds the conductor in a body ofinsulating material, as indicated at 8 in Fig. 7 and in the left-handportion of Fig. 3.

It will be observed that the two sheets or plates 1 and 2 are preciselyalike and are laid upon and secured to one another in such a manner thatthe edge of each plate projects beyond the corresponding edge of theother, thus allowing ready access to the ends of the resistance-coilsfor the purpose of connecting them to or disconnecting them from thehinding-screws 9, which pass through porcelain insulators 10, although,if desired, the hinding-screws may be dispensed with and the resistancepasseddirectly from one chamber into the next.

It is obvious that the supporting shell or plate may be made in onecontinuous piece, as shown at 11 in Fig. 6, instead of being made in twoseparate pieces, as above described. It is also obvious that whenradiation is desired from one side only a plate 12, of insulating orother material, such as slate, may be employed with a single corrugatedsheet 13 to hold the resistances 3 in the corrugations thereof.

I am aware that conductors have been enameled to plates of cast-iron;but the impracticability of this lies in the fact that castiron cannotbe enameled on its surface with a thoroughly-vitrified enamel, whereassheetiron or copper can. Enamel on the surface of cast-iron is porousand can and does absorb moisture. It is of the nature in that respect ofa brick, and as any glassy enamel placed upon the first coat becomes inpractice full of minute fissures or cracks the dampness or moisturefinds a very ready path to the absorbing coat of enamel and destroys theinsulation between the conductor and support. It is therefore seen thatsheet metal such as I use possesses advantages peculiar to itself andnot attained in the use of cast metals. It is also to be observed thatthere is a distinct difference between enameling or embedding in enamela conductor on the inside of a cylindrical support 14, as shown in Fig.'7, over enameling one on the outside from the fact that enamel beingavery brittle material will fly away from the metallic surface the momentany strain is brought to bear upon it in the right direction to tear ittherefrom, as in the case of a conductor being enameled on the outsideof, a cylinder. Here the moment the wire expands through the heatdeveloped by a current passing through it a strain is placed upon theenamel, tending to rupture it from the cylindrical body. In the event,however, ofa wire being enameled on the inside of a tube, as shown inFig. 7, for example, all the strain placed upon the enamel is backed upby the tube and there is no tendency for the enamel to break away.

In practice it is generally necessary to construct rheostats with stepsof different resistances, and in this case the last step thrown intocircuit beginningat low-resistance steps) is the one that generates themost heat. This is the case in a field-rheostat. In the case of amotor-starting rheostat or a theater-dimmer or a motor-regulator onlypart of the resistance is generally in circuit at one time. If each stepin the resistance were entirelyseparate, different parts of the rheostatwould have different temperatures, and some would have the atmospherictemperature. Now I make use of all of the radiating-surface at all timesby using supporting-shells for all or a number of the steps, which arein thermic contact from one end of the device, thereby distributing theheat evenly, and I preferably use copper sheets, which will conduct theheat rapidly from the hot parts of the device to cold parts, quicklyequalizing the temperature over the radiating-surface.

Iclaim as myinvention and desire to secure by Letters Patent- 1. In anelectric rheostat or heater, the combination of a metallic supportcomprising two plates having irregular outer surfaces and grooved innersurfaces, a layer of insulating material in said grooves, and a separateresistance-step in each groove, and an edge of one plate projectingbeyond the other to expose the ends of the resistances.

2. In an electric rheostat or heater, the combination of a metallicsupport comprising two plates having irregular outer surfaces andgrooved inner surfaces, a layer of insulating material in said grooves,a separate resistance-step in each groove, and an edge of one plateprojecting beyond the other to expose the ends of the resistances, and aseries of binding-posts mounted on the projecting edge and to which theresistance-steps are secured.

8. A rheostat or electric heater having a se ries of resistances, twosimilar, thin sheets of metal to inclose the resistances in closeproximity thereto, thin insulating material applied to the opposingfaces of said sheets, and means to secure said sheets together face toface with the edge of each projecting beyond the edge of the other toexpose the ends of the resistances.

4. In an electric rheostat or heater, the combination of two metallicplates having a series of grooves or corrugations, a layer of insulatingmaterial on the inner sides thereof, a separate resistance-step in eachgroove, said plates having the ends projecting beyond each other so asto expose the ends of the resistances, and binding-posts for saidresistances at the projecting ends of the plates.

